ABSTRACT
The acquisition of organelles and the evolution of compartmental boundaries have provided eukaryotes with unique mechanisms with which to modulate multiple cellular activities. This is particularly evident in the sequestration of chromosomes within a nuclear envelope, which effectively separates the nuclear processes of gene transcription and replication from translation. Clearly, control of molecular traffic across the nuclear envelope is a prerequisite for normal eukaryotic cell function. This enhanced regulatory potential in eukaryotes, however, comes at a cost of considerably complicating the mechanics of cell division. Progression through mitosis requires that chromosomes within the cell nucleus engage with microtubules (MTs) of the mitotic spindle. In organisms such as yeast, the spindle poles are embedded in the nuclear envelope (NE) and spindle MTs form within the nucleus. This is a ‘closed’ mitosis. In higher cells, however, the mitotic spindle is a cytoplasmic structure, and consequently, in order for mitotic chromosomes to align at the spindle equator, the NE must be either partially or completely dispersed.
